1. Field of the Invention
The present invention relates to a surface machining method and apparatus. More particularly, the present invention relates to a surface machining method and apparatus for brittle materials such as semiconductor materials, ceramics, glass, or the like.
2. Description of the Related Art
Loose abrasive for lapping, polishing, etc. is mainly used in mirror grinding for brittle materials such as semiconductor materials and ceramics. The loose abrasive is suitable for obtaining a flat and smooth surface; however, it is not suitable for the grinding which requires large throughput and high shaping accuracy. Since many wafers are ground at the same time in order to obtain the large throughput, the apparatus must be large-sized. Moreover, since the diameter of the wafer has been increased, there is a disadvantage in the accuracy of the lapping plate when the wafer of a large diameter is machined. Furthermore, the wafer cannot be efficiently machined by the loose abrasive.
In order to eliminate the above-mentioned disadvantages, a loose abrasive processing apparatus (e.g. a lapping apparatus and a polishing apparatus) which performs a single wafer processing is desired. Moreover, the transfer from the loose abrasive processing to the bonded abrasive processing has been desired.
In the conventional bonded abrasive processing, the center of the workpiece is machined only by the abrasive grains on the radius of the grinding wheel, which goes through the rotational center of the workpiece. For this reason, there are disadvantages in that the width of the grinding wheel is small, and if the machining speed is raised, the grinding resistance acting on each abrasive grain becomes larger. Furthermore, there are disadvantages in that the accuracy greatly depends on the state of the grinding wheel (the form and the dressing state); thus, the bonded abrasive processing is not suitable for the mirror grinding.
Furthermore, since the abrasive grains move on the same track, the movement of abrasive grains cannot be greatly changed even if the conditions such as the number of rotations, etc. are changed. The abrasive grains are concentrated on the rotational center of the workpiece, and the abrasive grains in the other area do not go through the rotational center of the workpiece. Thereby, there is a disadvantage in that warps are scattered on the surface.